Aluminium is known for its versatility; while properties such as superb resistance to corrosion and excellent thermal conductivity are very useful in many applications, it is the flexibility and adaptability of aluminium’s mechanical properties that make it such a widely used metal. The mechanical properties of aluminium can be altered through a variety of means (e.g. adding alloying elements or work hardening), but one of the most popular methods of altering the mechanical properties of some grades of aluminium is through tempering. Since tempering can have such a pronounced effect on an aluminium alloy, it is extremely important to be able to comprehend what the tempering designations of aluminium are and what they mean so that misunderstandings do not result in fracturing and failure.

What is an Aluminium Tempering Designation?

An aluminium tempering designation is a series of letters and numbers that are used to denote what type of tempering treatment an aluminium alloy has undergone. The temper designation is preceded by a dash and placed after the aluminium alloy designation (e.g. 6061-T6). Understanding what an aluminium temper designation means is critical to picking the correct material. It is important because an aluminium alloy can be exactly the same in terms of chemical makeup as another aluminium alloy, but if the two have different tempering designations, then the mechanical properties of both alloys could be vastly different.

What are the Aluminium Tempering Designations?

There are four main types of aluminium tempering designations. The types are denoted by a letter that precedes a number. The four letter designations are:

  • T: Thermally treated
  • H: Strain hardened
  • O: Annealed
  • F: As fabricated

Following the letters of an aluminium temper designation are numbers. The numbers specify exactly how the tempering method was performed. For instance, a T5 and a T6 are both thermally treated, however, a T5 indicates that the aluminium alloy was cooled from a high-temperature shaping process and artificially aged whereas a T6 was solution heat treated, and then artificially aged. The difference in a number in an aluminium temper designation can inform the purchaser of an aluminium alloy about a nuance that could have a significant impact on the mechanical properties of the alloy.

While there are many variations of numbers that can be used, the “T” number variations are perhaps the most commonly used and important to be understood. Here are descriptions of some of the “T” designation number variants:

  • T1: Naturally aged after cooling from an elevated temperature from a forming process
  • T2: Cooled from an elevated temperature forming process, cold worked, then naturally aged
  • T3: Solution heat treated, cold worked, then naturally aged
  • T4: Naturally aged after a solution heat treatment
  • T5: Artificially aged after cooling from an elevated temperature from a forming process
  • T6: Artificially aged after cooling from a solution heat treatment
  • T7: Solution heat treated then over-aged
  • T8: Solution heat treated, cold worked, then artificially aged
  • T9: Solution heat treated, artificially aged, then cold worked
  • T10: Cooled from an elevated temperature forming process, cold worked, then artificially aged

For the meaning of the numbers that follow letter temper designations such as “O”, “W”, and “F”, it is best to get a technical data sheet on aluminium alloy to determine exactly what the temper designation means.

Some Common Examples of Aluminium Alloy Tempers and Their Applications

Many different temper designations exist for a variety of aluminium alloys, but some are more prevalent than others, especially for certain uses. Here are some of the most popular aluminium alloy temper designations and their applications:

  • 2024-T4: Aircraft structures, fasteners, hardware, wheels, screw machine products
  • 3003-H14: Food and chemical handling equipment, tanks, trim, litho sheet, pressure vessels, and pipes
  • 5052-H32: Aircraft fuel/oil lines, fuel tanks, transportation, appliances, lighting, wire, and rivets
  • 6061-T6: Aircraft fittings, camera lens mounts, couplings, marines fittings and hardware, electrical fittings and connectors, decorative or misc. hardware, hinge pins, magneto parts, brake pistons, hydraulic pistons, appliance fittings, valves and valve parts
  • 6063-T5: Pipes, railings, furniture, architectural extrusions, irrigation pipes, and transportation
  • 7075-T6: Aircraft fittings, gears and shafts, fuse parts, meter shafts and gears, missile parts, regulating valve parts, worm gears, keys, aircraft, aerospace and defense applications; bike frames, all terrain vehicle (ATV) sprockets

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